Foaming in aqueous systems causes various kinds of problems in production processes in various industries, such as a decrease in productivity, an increase of defective products, a decrease in the packing ratio of products, and the like. In the pulp production industry, large amounts of foam producing substances are contained in the process water which result in the formation of problem-causing foam.
In the Kraft pulping process, pulp (wood chips) is cooked under pressure in a mixed solution of sodium hydroxide and sodium sulfide and everything other than the fiber in the wood is removed and dissolved in the solution to obtain the pulp product. The process water from the digestion process, typically referred to as black liquor, contains large amounts of sodium salts of the lignin and other components including resin.
These components possess foam forming properties during the separation process from the pulp and therefore cause problems during the pulp production process. This problem is also realized when the above-described black liquor, which remains in the separated pulp, is washed from the pulp.
Thus, as described above, the foaming caused during the pulp washing and screening processes after the digestion of the pulp feedstock results in a decrease in the efficiency of the pulp forming process. Similarly, the foaming which occurs in the papermaking process also causes various problems, such as a decrease in the strength of the paper produced, the quality of the paper made due to the presence of spots thereon, and breaks in the paper while travelling through the paper machine.
Various types of defoaming agents are presently being used in the pulp and paper manufacturing industries. However, high temperature defoaming agents are primarily oil based, either silicone and/or mineral, and are thus not environmentally friendly. Also, since they are oil based they are not readily water dispersable, resulting in their coagulation during the pulping and/or papermaking processes.
It is thus an object of the present invention to provide a defoaming composition and process which, while effective, is environmentally friendly, especially with regard to process waters with elevated temperatures.